A planet has been discovered orbiting our closest neighbour star and that planet could be at the right distance from its star and temperature for liquid water and the possibly of life to exist.

The star is called Proxima Centauri, a red dwarf that’s part of the Alpha Centauri system. This triple star system is just 4.2 light-years away from our Solar System. The three stars in the Alpha Centauri system are Alpha Centauri A, Alpha Centauri B and Alpha Centauri C (Proxima). Alpha Centauri A and B are a close pair of stars similar to our Sun but Alpha Centauri C (Proxima) is a small Red Dwarf star that appears to be orbiting the A – B pair at a much greater distance. Proxima is the closest of the triplet to us and the closest known star to us.

The Alpha Centauri stars compared to our Sun

The newly discovered planet is called Proxima b and it is a terrestrial world (Earth like) whose existence has now been confirmed after 16 years of study. It is not yet known whether Proxima b has an atmosphere or liquid water. However the computer models don’t rule out the possibility. That would make it the closest known exoplanet to us and the closest known exoplanet with the potential for life to exist. Scientists have suggested that for planets to be capable of supporting life they should orbit their star in what is known as the habitable zone where liquid water can exist. They call this the Goldilocks Zone (where it is not too hot and not too cold).

The habitable zone around Proxima where liquid water can exist

The planet is at least 30 percent more massive than Earth and makes one circuit around Proxima Centauri every 11.2 Earth days. These figures imply that the planet comes as close as 7.4 million kilometres to its parent star. If Proxima Centauri were like our Sun, the planet would be blazingly hot but because red dwarfs are much dimmer, scientists estimate Proxima b should have an Earth-like range of temperatures, from -30°C on its dark side to +30°C on its light side. That would make it possible for water to exist in liquid form on the surface which astrobiologists regard as a key requirement for life.

The scientists’ calculations assume that the planet might have an Earth like, heat-trapping atmosphere and that the planet’s rotation is tidally locked so that one side is constantly facing the star. At the moment we don’t know if the planet does have water but it does orbit at a distance from the star that would allow water to exist.

As new, more powerful and advanced telescopes come into service we should be able to determine if Proxima b has an atmosphere and even the composition of that atmosphere. This can be done by observing the light from the star as the planet passes across the disc of the star. It would then be possible to digitally subtract the light being received directly from the star but leaving the light that has passed through any atmosphere around the planet.

The expanded spectrum of our Sun (strips from top to bottom, left to right)

Detailed analysis of the composition of the atmosphere could even reveal signs of life. This can be done by analysing the spectrum of the light passing through the atmosphere. Discreet colours are absorbed by the atoms of each element in the atmosphere leaving dark lines on the spectrum. See the spectrum of our Sun above. The patterns of the dark lines can be identified to reveal each element that is present in the atmosphere. If Oxygen is found then this could indicate that life might be present. Oxygen is readily combined with many atoms that would quickly remove any naturally occurring Oxygen from the atmosphere. On Earth the Oxygen in our atmosphere is replenished by the photosynthesis process by plants. This would only identify the type of life we have on Earth but this is the only kind of life we know.